Transducer resistor shunt structure for low-cost probing

ABSTRACT

Embodiments described herein generally relate to resistive shunt design in a read sensor for providing accurate measurements from an electronic lapping guide (ELG). More specifically, embodiments described herein relate to a transducer resistor shunt structure for low cost probing. A bleed resistor network for a read sensor may comprise one or more first resistors arranged in parallel with one another and a second resistor arranged in series with the one or more first resistors. The resistor arrangement may require a small physical area and reduce or prevent ELG measurement errors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/096,725, filed Dec. 4, 2013, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to usingelectronic lapping guides to set a read sensor's stripe height, or morespecifically, to increasing shunt resistance when monitoring theelectronic lapping guides.

2. Description of the Related Art

A typical magnetoresistive (MR) read head includes an MR read sensor,which is located between first and second shield layers. When the readsensor is subjected to positive and negative signal fields from trackson a rotating magnetic disk in a disk drive, the resistance of the readsensor changes. These resistance changes cause potential changes in asense current flowing through the read sensor, which are processed asplayback signals by processing circuitry.

The read sensor has an exterior surface that faces the rotating magneticdisk and is supported on an air bearing from the rotating disk. Thisexterior surface is referred to as an air bearing surface (ABS). Theread sensor has a back edge that is recessed in the read head oppositethe air bearing surface. During fabrication, the ABS is defined so thatthe read sensor has a precise stripe height—i.e., the distance betweenthe ABS and the back edge. This is accomplished by lapping (grinding) awafer on which the MR head is constructed until the desired stripeheight is achieved.

One technique for determining whether the read sensor has the desiredstripe height involves transmitting a current through the read sensorand measuring the change in resistance as the ABS is lapped. However,the materials of the read sensor may introduce noise into the currentthat makes this technique unreliable. Instead, an electrical elementcalled an electronic lapping guide (ELG) may be fabricated on the readhead proximate to the read sensor. Moreover, the ELG may be made ofsimilar materials and have similar dimensions as the read sensor. Forexample, the ELG may be formed in the same photo and subtractiveprocesses as the read sensor to make the elements co-planar. Thus, asthe ABS is lapped, the dimensions of the ELG and the read sensor areaffected in a similar manner. Moreover, the materials of the ELG may beselected such that a current flowing through the ELG reliably indicatesthe changing resistance as the lapping process grinds the ABS—i.e., theELG, when lapped, generates a signal with less noise relative to theread sensor. The resistance of the ELG may be correlated with aparticular stripe height. Once the resistance that correlates to thedesired stripe height is achieved, the lapping is stopped. Because ofthe shared physical dimensions of the ELG and the read sensor, a readsensor proximate to the ELG is assumed to have the same stripe height asthe ELG.

An ELG may further comprise probe contacts for precise control andmeasurement of the lapping process. As structures are becomingincreasingly smaller, probing the ELG pads becomes problematic as theELG and transducer pads are present in increasingly reduced dimensions.Due to physical size limitations, bonding of the ELG often inadvertentlycontacts the component pads. If a read pad is in contact when probingthe ELG pad and the read transducer has resistive shunts to the systemground, errors in the ELG measurements may result.

A known solution is to increase the read transducer's shunt resistance.However, the materials used to cause the increase in the resistor shuntlayout occupy an extremely large portion of the slider area and areimpractical to implement as there is a desire for increasingly smallerdevices. Another solution may be to user higher-cost probe connectionsthat support a finer pitch/spacing resolution such that probing both theELG pad and another pad is not possible. However, this solution isgenerally more expensive to implement, and thus, generally undesirable.

Therefore, what is needed in the art is a transducer resistor shuntstructure for reliable and low cost probing.

SUMMARY OF THE INVENTION

Embodiments described herein generally relate to ELG's and associatedprobing contacts. More specifically, embodiments described herein relateto a transducer resistor shunt structure for low cost probing.

In one embodiment, a bleed resistor network for a read sensor isprovided. The bleed resistor network may comprise two first resistors inparallel with one another, wherein each of the first resistors have asubstantially equal impedance of greater than about 5 KOhms and a secondresistor arranged in series with the two first resistors, wherein thesecond resistor has an impedance of greater than about 250 KOhms.

In another embodiment, a device is provided. The device may comprise asubstrate and a plurality of read heads disposed on the substrate. Afirst one of the plurality of read heads may comprise a read sensorhaving a bleed resistor network comprising two first resistors inparallel with one another, wherein each of the first resistors have asubstantially equal impedance of greater than about 5 KOhms and a secondresistor arranged in series with the two first resistors, wherein thesecond resistor has an impedance of greater than about 250 KOhms. Anelectronic lapping guide (ELG) may also be provided. The ELG may beconfigured to indicate, based on a resistance of the ELG, a stripeheight of the read sensor.

In yet another embodiment, a system is provided. The system may comprisea substrate comprising a plurality of read heads. Each read head maycomprise a read sensor configured to sense data stored in a magneticmedia. A bleed resistor network of the read sensor may comprise twofirst resistors in parallel with one another, wherein each of the firstresistors have a substantially equal impedance of greater than about 5KOhms and a second resistor arranged in series with the two firstresistors, wherein the second resistor has an impedance of greater thanabout 250 KOhms. An ELG may be configured to indicate, based on aresistance of the ELG, a stripe height of the read sensor. The ELG maybe electrically coupled to the substrate. A bonding pad may beelectrically coupled to the ELG. The bonding pad, ELG, and the substratemay be part of a current path permitting current to flow through theELG. A lapping unit may be configured to simultaneously lap an airbearing surface on the plurality of read heads. The substrate may bemounted on the lapping unit. A lapping controlled may be electricallycoupled to the bonding pad and the substrate. The lapping controller maybe configured to measure the resistance of the ELG using the currentpath and transmit instruction to the lapping unit based on the measuredresistance.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 illustrates a disk drive system, according to certain embodimentsdescribed herein.

FIGS. 2A-2B illustrate a portion of a read head with an ELG for settinga stripe height, according to certain embodiments described herein.

FIG. 3A illustrates a wafer with a plurality of read heads, according tocertain embodiments described herein.

FIG. 3B illustrates lapping a row of read heads based on a measuredresistance of one or more ELGs, according to certain embodimentsdescribed herein.

FIGS. 4A-4B illustrate schematic circuit model diagrams of an electricalcircuit that includes the substrate on which the read sensor isdisposed, according to certain embodiments described herein.

FIGS. 5A and 5B are schematic illustrations of bleed resistor networksfor ELG connections.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

In the following, reference is made to embodiments of the invention.However, it should be understood that the invention is not limited tospecific described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practice theinvention. Furthermore, although embodiments of the invention mayachieve advantages over other possible solutions and/or over the priorart, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the invention. Thus, the followingaspects, features, embodiments and advantages are merely illustrativeand are not considered elements or limitations of the appended claimsexcept where explicitly recited in a claim(s). Likewise, reference to“the invention” shall not be construed as a generalization of anyinventive subject matter disclosed herein and shall not be considered tobe an element or limitation of the appended claims except whereexplicitly recited in a claim(s).

Embodiments described herein generally relate to resistive shunt designin a read sensor for providing accurate measurements from an ELG. Whenlapping the ABS of a read head (or a plurality of read heads), theelectrical resistance of the ELG is used to adjust the lapping processand set the stripe height for a read sensor in the read head.Specifically, as an exterior surface of the ELG at the ABS is lapped,the resistance of the ELG increases. Once the resistance corresponds tothe desired stripe height—i.e., the distance between the ABS and theback edge of the read sensor—the lapping process is stopped. To measurethe electrical resistance of the ELG, a lapping controller may be wirebonded to at least one pad on the read head that electrically connectsthe controller to the ELG. In addition to being connected to the pad,the ELG is electrically connected to an electrically conductivesubstrate on which the read head is disposed. The substrate may be usedas a common ground for the current that flows through the bond pad andthe ELG.

Because many read head fabrication techniques lap a plurality of readheads simultaneously, each ELG in the read heads may be electricallycoupled to the substrate—i.e., share the same ground plane. The lappingcontroller is then wire bonded to the individual ELGs via respectivepads, but the controller is connected to the substrate only at a fewlocations. For example, the lapping controller may be wire bonded tothirty ELGs in a row of read heads but only have one or two electricalconnections to the conductive substrate. The resistances of each of theconnected ELGs can be monitored by sweeping through the different wirebond connections. In contrast, if a shared common ground is not used(i.e., current does not flow through the substrate) the lappingcontroller couples to two pads per read head in order to measure theresistance of the ELG. When using a shared ground connection to thesubstrate, however, the lapping controller may be connected to only onebond pad for each ELG of interest.

FIG. 1 illustrates a disk drive 100 according to certain embodimentsdescribed herein. As shown, at least one rotatable magnetic disk 112 maybe supported on a spindle 114 and rotated by a disk drive motor 118. Themagnetic recording on each disk may be in the form of annular patternsof concentric data tracks (not shown) on the magnetic disk 112.

At least one slider 113 may be positioned near the magnetic disk 112,each slider 113 supporting one or more magnetic head assemblies 121. Asthe magnetic disk 112 rotates, the slider 113 moves radially in and outover a disk surface 122 so that the magnetic head assembly 121 mayaccess different tracks of the magnetic disk 112 where desired data iswritten. Each slider 113 may be attached to an actuator arm 119 by wayof a suspension 115. The suspension 115 may provide a slight springforce which may bias the slider 113 against the disk surface 122. Eachactuator arm 119 may be attached to an actuator 127. The actuator 127,as shown in FIG. 1, may be a voice coil motor (VCM). The VCM comprises acoil movable within a fixed magnetic field, the direction and speed ofthe coil movements being controlled by the motor current signalssupplied by a control unit 129.

During operation, the rotation of the magnetic disk 112 generates an airbearing between the slider 113 and the disk surface 122 which exerts anupward force or lift on the slider 113. The air bearing thuscounter-balances the slight spring force of the suspension 115 andsupports slider 113 off and slightly above the disk 112 surface by asmall, substantially constant spacing during normal operation.

The various components of the disk drive 100 are controlled in operationby control signals generated by control unit 129, such as access controlsignals and internal clock signals. Typically, the control unit 129comprises logic control circuits, storage, and a microprocessor. Thecontrol unit 129 generates control signals to control various systemoperations, such as drive motor control signals on line 123 and headposition and seek control signals on line 128. The control signals online 128 provide the desired current profiles to optimally move andposition slider 113 to the desired data track on disk 112. Write andread signals are communicated to and from write and read heads on theassembly 121 by way of recording channel 125.

The above description of a typical magnetic disk storage system and theaccompanying illustration of FIG. 1 are for representation purposesonly. It should be apparent that disk storage systems may contain alarge number of disks and actuators, and each actuator may support anumber of sliders.

FIGS. 2A-2B illustrate a portion of a read head with an ELG for settinga stripe height, according to embodiments described herein. FIG. 2Aillustrates a portion of the magnetic head assembly 121 where theassembly 121 includes a portion of a read head 205 and a conductivesubstrate 210. The read head 205 includes a plurality of differentlayers that may be used to form, for example, a plurality of shieldlayers and a read sensor (not shown). The read sensor may be amagnetoresistive sensor such as giant magnetoresistance (GMR) sensor ora tunneling magnetoresistance sensor (TMR) where the electricalresistance of the read sensor is measured to identify a change inmagnetic orientation of the magnetic material in the associated disk.For example, the read sensor may be a current-perpendicular-to-the-plane(CPP) GMR sensor or a TMR sensor formed by lapping an ABS.

FIG. 2A illustrates a side view of the magnetic assembly 121 where otherelements of the read head 205 are omitted. Specifically, FIG. 2Aillustrates only the components used in the assembly 121 to connect anELG 215 to an electrical circuit. A lapping controller (not shown) maybe electrically coupled to the ELG 215 by connecting a conductive wire(e.g., gold or copper wire, or other highly conductive material) to abonding pad 220. The connective material 225 (e.g., a melted portion ofa bond wire, a solder bump, conductive paste/epoxy, ultrasonic bonding,and the like) may be used to physically and electrically couple the wire230 to the pad 220. A first internal lead 235 connects the bonding pad220 to a first side of the ELG 215 thereby electrically connecting theELG to an external lapping controller. A second internal lead 240connects a different side of the ELG 215 to the conductive substrate 210(e.g., titanium carbide/alumina, or other suitable conductive material).The read head 205 may include a third internal lead 245 that connectsthe substrate 210 to the grounding pad 250. In one embodiment, thesecond internal lead 240 and third internal lead 245 may be combinedinto the same lead. Like the bonding pad 220, the grounding pad 250 mayalso be connected to the lapping controller using connective material255 and a conductive wire 260. In this manner, the lapping controllermay use a voltage source to provide a potential difference between thegrounding pad 250 and the bonding pad 220 which generates a currentthrough the ELG 215. Alternatively, the lapping controller may source acurrent between the pads 250 and 220 and measure the resulting potentialdifference.

FIG. 2B illustrates a top view of the read head 205. The arrow 265illustrates a direction where the ELG 215 is polished during the lappingprocess. That is, arrow 265 illustrates an exterior surface of the ELG215 that is formed into an ABS by the lapping process. During thisprocess, the surface of the ELG 215 on the ABS is lapped or polished byan abrasive surface which decreases one or more physical dimensions ofthe ELG 215. As a physical dimension of the ELG 215 (e.g., its height)is decreased by the lapping process, the current flowing through the ELG215, and thus, the resistance of the ELG 215 is changed. Decreasing thesize of the ELG 215 reduces the amount of area in which the current canflow, thereby increasing the electrical resistance. The lappingcontroller measures the resistance based on the current flowing throughthe ELG 215 and determines a corresponding stripe height 275 based onthe resistance. For example, assume that the ELG 215 is 6 μm wide, 10 nmthick, and 100 nm tall. These dimensions may correspond to a measuredresistance of 250 ohms (Ω). However, after performing the lappingprocess, the ELG 215 is 6 μm wide, 10 nm thick, and only 50 nm tallwhich may correspond to a resistance of 500Ω. The lapping controller maybe preconfigured to contain a data structure that correlates a measuredresistance to the physical dimensions of the ELG 215. Although theembodiments presented herein discuss lapping as the chosen method forforming the ABS and setting the stripe height 275, other planarizationtechniques may be used to set the stripe height 275.

FIG. 2B also illustrates a read sensor 270 in the read head 205 which isnot shown in FIG. 2A. The read sensor 270, like the ELG 215, may includean exterior surface on the ABS which is polished by the lapping processas shown by arrow 265 and may have the same physical dimension as theELG 215 and related locations in the read head 205, such as beingco-planar. The ELG 215 may include a plurality of materials that aresimilar to the materials in a read sensor in the read head 205. However,the ELG 215 may be fabricated differently from the read sensor such thatthe ELG 215 generates a signal during lapping that can be used by thelapping controller to identify the resistance of the ELG 215. Incontrast, if the lapping controller were connected to the read sensor270 during the lapping process, the electrical properties of thematerials in the read sensor 270 (or the arrangement of those materials)prevent the lapping controller from accurately identifying theresistance of the read sensor 270. Specifically, in some embodiments,the structure of the read sensor 270 may be prone to smearing shuntsduring lapping, and thus, is unsuitable for controlling the lappingprocess. By fabricating the ELG 215 to include the similar materials aswell as similar physical dimensions as the read sensor 270, both the ELG215 and the read sensor 270 are similarly changed during the lappingprocess. Thus, the ELG 215 may serve as a proxy to the read sensor 270where the height or the resistance of the ELG 215 is imputed to the readsensor 270. That is, either the height or the resistance of the ELG 215may be used to derive the current stripe height 275 of the read sensor270.

In other embodiments, the grounding pad 250 may not be connected to thelapping controller. For example, the lapping controller may insteadconnect to the substrate 210 at a portion of the top surface of thesubstrate 210 that is not covered by the read head 205. This may enablean electrical connection from the lapping controller and the substrate210 with less electrical resistance because the third internal lead 245and the grounding pad 250 may be omitted or substituted by electricalelements with smaller resistances.

The embodiments disclosed herein, however, are not limited to anyparticular type or method of fabricating the ELG 215. Indeed, thepresent embodiments may use any ELG 215 so long as the ELG 215 can beused to derive the stripe height 275.

FIG. 3A illustrates a wafer 300 with a plurality of read heads 305formed thereon. The wafer 300 includes a substrate 210 that is processedto include the plurality of read heads 305. For example, a single wafer300 may include hundreds of different read heads 305 with individualELGs and read sensors. In certain embodiments, 60 read heads 305 may beutilized. Before lapping the read heads 305 to set the stripe height ofthe read sensors, the wafer 300 may be cleaved or diced (using a saw)into individual rows. The ghosted portion illustrates a row 310 of theread heads 305 that may be separated from the rest of the read heads305.

FIG. 3B illustrates lapping a row 310 of read heads based on a measuredresistance of one or more ELGs, according to one embodiment describedherein. The row 310 diced from the wafer 300 shown in FIG. 3A is mountedinto the lapping system or unit 350. As shown, the row 310 includes aplurality of read heads 205A-205H. Only eight read heads are shown, butthe number of read heads per each row may vary depending on theparticular portion of the wafer the row was diced from. Accordingly,each row 310 may include only one read head or even one hundred or moreread heads. Each read head 205A-205H may include two external bondingpads: a grounding pad 250 and a bonding pad 220. Although each read head205A-205H includes both types of pads, in other embodiments only certainread heads may have grounding pads 250 (e.g., only the read heads 205Aand 205H at the end of the row 310. Additionally or alternatively, onlya subset of the read heads 205A-205H in a row 310 may have bonding pads250. Regardless of how the pads 220, 250 are distributed amongst thedifferent read heads 250A-205H, the bonding pads 220 connect to one sideof an ELG in the sensor heads 250A-205H while the grounding pads 250provide a connection to the substrate 210 of the row 310.

The lapping system 350 may include an abrasive pad 355, a force system360, and a lapping controller 385. The abrasive pad 355 may include oneor more separate pads that rub against the ABS of the read heads205A-205H, thereby removing portions of the ABS and reducing the heightof the read sensors as shown in FIG. 2B. The abrasive pad 355 may be anabrasive material such as diamond particles, aluminum oxide, or siliconcarbide that grinds or laps away the portion of the read heads 205A-205Hthat the pad 355 contacts. Alternatively, the abrasive pad 355 may be asofter material such as tin that is “charged” with an abrasive to lapthe ABS.

The force system 360 may include an actuator 380, pistons 375, rods 370,and a buffer 365. The actuator 380 is communicatively coupled to thelapping controller 385 and receives instructions for separatelycontrolling the respective pistons 375. As such, the actuator 380 mayuse the pistons 375 to determine how much force to apply to differentportions of the row 310. The pistons 375 may be electrically,magnetically, pneumatically, or hydraulically controlled to apply aspecified pressure or force to the buffer 365. The buffer 365, asemi-flexible material such as polyurethane, may transfer the force to arespective portion of the row 310. By increasing the force applied by aparticular piston 375, the actuator 380 controls the rate at which theabrasive pad 355 grinds a read head or group of read heads 205. Here,each piston 375 is associated with two read heads 205A-205H althougheach piston 375 may be assigned to more or less read heads. If theactuator 380 is informed by the lapping controller 385 that some subsetof the read heads 205A-205H are being lapped at a different rate by theabrasive pad 355 relative to another portion, then the actuator 380 canadjust the associated pistons 375 to correct the imbalance.

The lapping controller 385 (e.g., a printed circuit board or other logiccontaining computing element) may be used to determine the lap rate ofthe different read heads 205A-205H and instruct the actuator 380 tocorrect any imbalance or stop the lapping process when the desiredstripe height is achieved. As shown, the lapping controller 385 may beelectrically coupled (e.g., wire bonded) to every other read head in therow 310, i.e., read heads 205B, 205D, 205F, and 205H, using the bondingpads 220. However, the lapping controller 385 may be coupled to more orless than this ratio. In one embodiment, the lapping controller 385 maybe coupled to as many read heads as there are pistons 375 in theactuator 380. That is, the lapping system 350 may designate one of theread heads associated with a piston 375 as the representative head(e.g., read heads 205B, 205D, 205F, or 205H) which is coupled to thelapping controller 385. The resistance of the ELG in the representativeread head is then measured and used by the lapping controller 385 tocontrol the associated piston 375. However, to improve control, in otherembodiments the lapping controller 385 may be coupled to two or more ofthe read heads 205 associated with a single piston 375 and control thepiston 375 based on measuring the resistance of both of the ELGs in thetwo or more heads. For example, the lapping controller 385 may averagethe measured resistances of the ELGs and use the average resistance toderive the stripe height and control the piston pressure.

When lapping, the lapping controller 385 may iteratively apply a voltageor source a current to each connected read head 205B, 205D, 205F, and205H using the respective bonding pads 220 and the grounding pad 250 ofread head 205H. Because the connected read heads 205B, 205D, 205F, and205H share the same ground connection, the lapping controller 385 maymeasure the resistances of the ELGs in each of the read heads 205B,205D, 205F, and 205H sequentially during non-overlapping intervals.Based on the measured resistances, the lapping controller 385 sendsadjustment instructions to the actuator 380 for changing the pressureapplied by the pistons 375. For example, if the resistance associatedwith read head 205H is greater than the resistances of the other readheads coupled to the lapping controllers 385, the actuator 380 mayreduce the pressure applied by the actuator 380 associated with readhead 205H (or increase the pressure applied by the pistons 375associated with the other read heads 205B, 205D, and 205F).

FIGS. 4A-4B illustrate schematic circuit model diagrams of an electricalcircuit that includes the substrate 210 on which the read head isdisposed, according to embodiments described herein. Specifically, FIG.4A illustrates a circuit model 400 for a row of read heads, however, forclarity, the connections between other read heads in the row and thelapping controller 385 have been omitted. The circuit model 400 includestwo ground connections 402 for connecting the lapping controller 385 tothe substrate 210 via two different grounding pads 250. The lappingcontroller 385 includes a voltage source 405 which provides a voltagepotential between the grounding pads 250 and the bonding pad 220, suchas a component bonding pad. The voltage potential results in currentflowing between the pads 220, 250 and through the element (i.e. TMRelement) which is here modeled as a bleed resistor network R_(TMR).

The ELG is also present on the substrate 210 and an ELG bond pad 420 iscoupled to the controller 385 by an ELG bond 404. Although the ELG bond404 is intended to connect the ELG bond pad 420 and the lappingcontroller 385, the ELG bond 404 may inadvertently touch the bonding pad220 which may result in an error measurement during the lapping process.

The resistive network R_(TMR) may comprise one or more resistors, suchas resistors R₁, R_(1′), and R₂. Resistor R₁ and resistor R_(1′) may bearranged in parallel to each other and may exhibit substantially equalimpedance. The impedance of each of resistor R₁ and resistor R_(1′) maybe between about 5 KOhms and about 50 KOhms, such as about 20 KOhms. Forexample, the element may be shunted by approximately 40 KOhms which maybe the combined impedance of resistor R₁ and resistor R_(1′). ResistorR₂ may be arranged in series with resistors R₁ and R_(1′). Resistor R₂may have an impedance of between about 250 KOhms and about 750 KOhms,such as about 510 KOhms. The R_(TMR) circuit 400 may provide for theelement's resistance to the substrate 210 being dominated by resistorR₂. As such, the element may not be shunted by resistors R₁ and R_(1′).In certain embodiments, the circuit 400 may be referred to as aseries-parallel-shunt (SPS). The SPS design may occupy a lesser physicalarea compared to conventional circuit designs, which may allow for evensmaller elements and associated lapping guides.

FIG. 5A depicts a bleed resistor network layout according to certainembodiments described herein. As previously described, resistors R₁ andR_(1′) are arranged in parallel with one another and resistor R₂ isarranged in series with resistors R₁ and R_(1′). The R₁ and R_(1′) arecoupled via bonds 504 to the element, such as the reader, and theresistor R₂ is coupled to the substrate 210, more precisely, a slider500, via a bond 502. The physical area occupied by the bleed resistornetwork on the slider 500 is substantially reduced when compared to aconventional bleed resistor network, such as the bleed resistor networkshown in FIG. 5B. For example, the conventional bleed resistor networkof FIG. 5B requires two resistors in parallel with one another and eachresistor may provide an impedance of 1 MOhm. Each resistor is coupledvia bond 504 to the element and the resistor network requires two bonds502 for connection to the slider 500 As may be seen, the physical arearequired to form two 1 MOhm resistors is substantially greater than thearea required by the bleed resistor network of FIG. 5A utilizing the SPSarrangement.

Referring back to FIG. 4A, the voltage source 405 may transmit DCsignals, AC signals, or some combination of both. When transmitting anAC signal, the voltage source 405 may use any type of waveform such assquare, sinusoidal, sawtooth, and the like. The resistance module 410may be coupled to the voltage source 405 such that the module 410 isinformed of the voltage being applied in the circuit 400. Based on ameasured current or a measured voltage if a current source is used, theresistance module 410 may then derive the value of the ELG. However, theELG value may be distorted by the parallel shunting of the R_(TMR). FIG.4B illustrates a simplified circuit model 401 where the voltage source405 is coupled to a particular ELG, and inadvertently to the element(read head) in the row 310. A positive side of the voltage source 405 isshown connected to R_(TMR) while a negative side of the voltage source405 is coupled to a common ground node, such as the substrate 210. Asshown, the total resistance of the bleed resistor network R_(TMR)(R₁/R_(1′) in parallel with R₂ in series—SPS shunt) is much greaterrelative to the resistance of the ELG. Thus, it is believed that themeasured resistance is dominated by the resistance of the ELG and theinadvertent ELG-sensor bonding overlap will not create substantial errorin the lapping measurement.

Embodiments described herein generally relate to an ELG circuit designlapping having an SPS arrangement with a relatively small layout arearequirement. When lapping the ABS of a read head (or a plurality of readheads), the electrical resistance of the ELG is used to adjust thelapping process and set the stripe height for a read sensor in the readhead. Specifically, as an exterior surface of the ELG at the ABS islapped, the resistance of the ELG increases. Once the resistancecorresponds to the desired stripe height—i.e., the distance between theABS and the back edge of the read sensor—the lapping process is stopped.The SPS circuit arrangement may provide an equal amount of parallelshunt protection while providing additional resistance to ground toavoid ELG measurement errors. The SPS circuit arrangement also requiresless physical area than conventional shunting circuitry for a bleedresistor network.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A bleed resistor network for a read sensor, comprising: two first resistors connected in parallel with one another, wherein each of the first resistors have a substantially equal impedance; and a second resistor arranged in series with the two first resistors.
 2. The bleed resistor network of claim 1, wherein the impedance of each first resistor is about 20 KOhms.
 3. The bleed resistor network of claim 2, wherein the impedance of the second resistor is about 510 KOhms.
 4. The bleed resistor network of claim 1, wherein the combined impedance of the two first resistors is about 40 KOhms.
 5. A device, comprising: a substrate; and a plurality of read heads disposed on the substrate, a first one of the plurality of read heads comprising: a read sensor having a bleed resistor network, the bleed resistor network comprising: two first resistors in parallel with one another, wherein each of the first resistors have a substantially equal impedance; a second resistor arranged in series with the two first resistors; and an electronic lapping guide (ELG) configured to indicate, based on a resistance of the ELG, a stripe height of the read sensor.
 6. The device of claim 5, wherein the impedance of each first resistor is about 20 KOhms.
 7. The device of claim 6, wherein the impedance of the second resistor is about 510 KOhms.
 8. The device of claim 5, wherein the combined impedance of the two first resistors is about 40 KOhms.
 9. The device of claim 5, wherein the plurality of read heads are arranged in a row on the substrate.
 10. The device of claim 5, wherein the substrate comprises alumina or titanium carbide.
 11. The device of claim 10, wherein the read sensor comprises a tunneling magnetoresistance sensor or a giant magnetoresistance sensor.
 12. The device of claim 5, wherein the read sensor comprises a tunneling magnetoresistance sensor or a giant magnetoresistance sensor.
 13. A system, comprising: a substrate comprising a plurality of read heads, each read head comprising: a read sensor configured to sense data stored in a magnetic media, wherein a bleed resistor network of the read sensor comprises: two first resistors in parallel with one another, wherein each of the first resistors have a substantially equal impedance; a second resistor arranged in series with the two first resistors; an ELG configured to indicate, based on a resistance of the ELG, a stripe height of the read sensor, wherein the ELG is electrically coupled to the substrate; and a bonding pad electrically coupled to the ELG, wherein the bonding pad, the ELG, and the substrate are part of a current path permitting current to flow through the ELG; a lapping unit configured to simultaneously lap an air bearing surface on the plurality of read heads, wherein the substrate is mounted on the lapping unit; and a lapping controller electrically coupled to the bonding pad and the substrate, the lapping controller configured to measure the resistance of the ELG using the current path and transmit instructions to the lapping unit based on the measured resistance.
 14. The system of claim 13, wherein the impedance of each first resistor is about 20 KOhms.
 15. The system of claim 14, wherein the impedance of the second resistor is about 510 KOhms.
 16. The system of claim 13, wherein the combined impedance of the two first resistors is about 40 KOhms.
 17. The system of claim 13, wherein the plurality of read heads are arranged in a row on the substrate.
 18. The system of claim 13, wherein the substrate comprises alumina or titanium carbide.
 19. The system of claim 18, wherein the read sensor comprises a tunneling magnetoresistance sensor or a giant magnetoresistance sensor.
 20. The system of claim 13, wherein the read sensor comprises a tunneling magnetoresistance sensor or a giant magnetoresistance sensor. 